Microscale Liquid Decal Film is what I use to strengthen decals. I've used it on home-printed Inkjet decals, as well as older kit decals. I've had some very old decals (50 years) that it didn't sufficiently strengthen, so YMMV.

__________________
Paul
If we weren't all crazy, we would go insane - Jimmy Buffett
NAR #87246 www.wooshrocketry.org